Method for logging the performance of a vehicle suspension system

ABSTRACT

A method for logging the performance of a vehicle suspension system including the steps of measuring the dynamic effect of an impulsive load with an electronic weighing system, wherein the electronic weighting system is mounted onboard the vehicle, and determining one or more parameters selected from the group consisting of the dampening ratio of the suspension, the oscillation frequency of the suspension and the impact loading of the vehicle.

This application claims the benefit under 35 U.S.C. § 371 toInternational Application PCT/AU2004/001107, which claims the priorityof Australian Application No. 2003904423 filed Aug. 19, 2003.

FIELD OF THE INVENTION

The present invention relates to vehicle suspension systems and inparticular to a method for logging the performance of a vehiclesuspension system in reaction to impulsive loads applied thereto.

BACKGROUND ART

Methods for testing the performance of vehicle suspension systems aregenerally known.

Automotive vehicles commonly employ a suspension system connectedbetween the road wheels and the body of the vehicle.

Conventional shock absorbers typically have a limited operating life,and therefore may need to be replaced when they no longer functionproperly. In order to determine if a shock absorber needs to bereplaced, the simplest and most widely used conventional diagnostictesting approach typically involves a technician applying force to thevehicle fender, or elsewhere on the vehicle body, and visually detectingthe rocking movement response of the vehicle. The resulting oscillationsare often counted visually or by an oscillation measuring deviceattached to the vehicle. The conventional suspension testing approachtherefore involves subjective interpretation by the technician which maynot be consistently reliable.

As can be appreciated, this test cannot feasibly be applied to largevehicles such as road haulage trucks and the like.

Another test which may be applied is the European Drop Test, in which aset of axles is mounted on a test rig and is driven over an inclinedramp with a sheer drop of approximately 80 mm on its facing edge. Thedamping ratio and frequency of the suspension is then measured usingload cells attached to the test rig.

The results gained in the above manners may be inaccurate andinconclusive in that they do not accurately take into account thecombined effect of vehicle weight, suspension geometry and shockabsorber characteristics as they relate to the efficiency of the shockabsorber in maintaining the vehicle's wheel in contact with the roadsurface having regard to the road bumps which the vehicle normallyencounters. Also these simple tests do not take into account multipleaxles coupled together in what is commonly called a suspension group,for example, a tandem axle group, tri axle group, quad axle group, andthe like.

Other known devices for testing shock absorbers test the dynamicreactions of suspension. Some of these devices require the removal ofthe shock absorbers from the vehicle. This practice is highlyimpractical for two reasons. First, labour costs involved in the shockabsorber's removal for testing and subsequent reinstallation areprohibitive, in that such costs may be equal to or greater than the costof replacement shock absorbers. This is particularly true with shockabsorbers founded in MacPherson-type suspensions wherein removal of theshock absorber necessitates the disassembly of other suspensioncomponents, such as the spring, balljoint and brake assembly.

Second, testing of a shock absorber isolated from its operatingenvironment is believed to be unsatisfactory as its dampening ability ismeasured against an arbitrary standard rather than relative to thesuspension system of which it is a part. As the performance of the shockabsorber in conjunction with the rest of the suspension system affectsthe handling, ride, suspension performance, stability and safety of thevehicle, the practice of shock absorber testing as an isolated componentcan be seen to be unsatisfactory as a method of determining in-serviceperformance of the suspension, or a suspension group as a whole unit inan operating environment.

As the shock absorber must be removed from the vehicle in order to testit's performance using this test, the vehicle must be removed fromservice for the length of the tests. This results in a loss of profitsfor the owner operator while the vehicle cannot be used during theperiod of downtime.

Other devices currently on the market, namely those operating on theseismograph principal evaluate the suspension systems as a whole, butare restricted to recording movement of the vehicle's body withoutallowing the deduction of the dampening factor of the system, (i.e.,shock absorber performance).

With the advent of the Intelligent Access Project (IAP) under the NRTCguidelines and with the future introduction of Performance BasedStandards (PBS), haulage or freight trucks may be called upon to complywith these standards which relate to the performance of suspension andsuspension components, as a whole or as a group of axles, so equipped.Under the IAP and the PBS guidelines, the vehicle suspension may berequired to meet performance standards in order to maintain thecompliance of the vehicle and its fitness for service. This compliancetesting may test one or more parameters of the suspension whichdetermine the “road friendliness” of the suspension. A “road friendlysuspension” may be one which functions within predetermined limits forone or more of the parameters, and attaining or complying with “roadfriendliness” may provide advantages for the owner/operator of thevehicle such as the ability to carry heavier loads or access to roadswhich non-compliant vehicles may be restricted from using. As well, theroad friendly performance of the suspension/s will affect the workinglife of the road itself with attendant reduction in maintenance costsand increased safety to all road users, with the economic benefits ofsuch savings flowing on to the general community.

The compliance of the suspension is generally tested periodically overthe life of the vehicle or of the vehicle suspension.

It is therefore desirable to provide for an accurate test procedure fortesting the performance of suspension components on a vehicle todetermine whether the suspension is functioning properly and withinlegally acceptable limits while the vehicle is in use and withoutrequiring the removal of the vehicle from service. In addition, it isdesirable to provide for a test procedure for testing vehicle suspensioncomponents that does not require subjective interpretation by atechnician.

SUMMARY OF THE INVENTION

The present invention is directed to a method for logging theperformance of a vehicle suspension system, which may at least partiallyovercome the abovementioned disadvantages or provide the consumer with auseful or commercial choice.

In one form, the invention resides in a method for logging theperformance of a vehicle suspension system including the steps ofmeasuring the dynamic effect of an impulsive load with an electronicweighing system, wherein the electronic weighing system is mountedonboard the vehicle, and determining one or more parameters selectedfrom the group consisting of the dampening ratio of the suspension, theoscillation frequency of the suspension and the impact loading of thevehicle.

The method given above is preferably used to test the “roadfriendliness” of a suspension of vehicles. “Road friendliness” isassessed by the National Road Transport Commission (NRTC), and once aroad friendly standard has been attained, the vehicle is generallyallowed increased mass limits. The road friendliness of a suspension orsuspension group, that is two or more axles connected together for loadsharing as defined in the guidelines of the Higher Mass Limits (HML), isgenerally assessed under the current Higher Mass Limits (HML), currentlyin force, according to two criteria, namely the damping ratio of thesuspension and the frequency of oscillation of suspension in response toan impulsive load.

In order to be considered road friendly, suspensions must have a dampingratio of greater than 20 percent, meaning that the reduction in theamplitude of oscillations which suspension undergoes in response to animpulsive load should decrease by greater than 20 percent eachoscillation.

In addition to the required damping ratio in order to be considered roadfriendly, suspensions should have a frequency of oscillation of lessthan 2 Hz.

Preferably, components of an electronic weighing system mounted on boardthe vehicle may be used to measure and/or collect the data usedaccording to the method of the present invention to calculate thedamping ratio and frequency of oscillation. Typical electronic weighingsystems may comprise at least one load measuring element, usually a loadcell or pressure transducer, each associated with one or more suspensioncomponent. Each load cell or pressure transducer may also be associatedwith a signal amplifier. Each signal amplifier may be associated with acentral power module and a meter to display the data and/or the collatedresults of the tests performed.

According to a particularly preferred embodiment, the signal amplifiersused according to the present invention may be “smart” amplifiers. Theseamplifiers may be capable of storing the results of calibration testingproduced according to the invention. In this way, the calibrationresults are stored in each “smart” amplifier associated with each loadcell or pressure transducer and are therefore not dependent oninformation storage in the meter.

The meter may preferably include a display, generally located in thecabin of the vehicle allowing review or the data or results by a driver.The meter may also be associated with one or more remote display unitsand/or meters such as a computer allowing review of the informationgathered according to the method of the present invention, from alocation remote from the meter located in the cabin of the vehicle.

Preferably, each suspension component may be provided with a load cellor pressure transducer. Accordingly, a central meter may be provided towhich all load cells or pressure transducers transmit the data. Suchtransmission may be along cabling or may be wireless transmission ofdata.

Suitably, the meter may be a multi-channel meter capable of receivinginformation from up to eight or more channels. Preferably each of thechannels may receive data from an axle grouping. Further, up to eight ormore load cells and/or pressure transducers may provide information tothe meter on each channel. Therefore, a single meter may be capable ofreceiving and recording information from a total of up to at least 64load cells or pressure transducers.

Each meter or system may preferably comprise an on-board storage deviceeither built into the system or attached thereto such as a datalog/logger which suitably receives and records all information from allassociated load cells or pressure transducers. The data log/logger maypreferably allow the tracking of the information collected according todates, times, and particular dynamic parameters such as G-force andtime, both of which can be either pre-set or varied to suit particularoperating conditions and/or test conditions which may be varied toallow/achieve certain or specific data, according to either the owner'sinterests or that of a particular authority or body who has a right tosuch information. Accordingly, all data collected may be provided withan identification code allowing the tracking of the data.

Typically, the meter from a single vehicle may be capable ofcommunication with a tool for analysis of the collected information, theanalysis tool may be on-board either as a separate tool or built in tothe system. In order to transmit and/or receive the information, themeter or system in general, may be provided with a means fortransmitting and/or receiving information. The means for transmittingand/or receiving information may preferably be in the form of aninterconnecting cable, radio frequency data link, a telephonic link orany other type of the means for transmitting and receiving information.

According to the present invention, each vehicle utilising the method ofthe present invention may be provided with a vehicle locating means.According to a particularly preferred embodiment, the vehicle locatingmeans may preferably be a satellite global positioning system. However,other locating means, such as trip meters, may be used according to theinvention.

The method may utilise one or more remote interrogation units adapted toallow remote access to the meter provided in a vehicle. The remoteinterrogation units may allow the viewing and/or analysis of informationcollected on a real time basis, or on a later time basis, that is, atthe discretion of the operator or the body requiring such data.

According to a first particularly preferred embodiment of the invention,the performance of the vehicle suspension system is logged over astandard or specific road section at different times. This performancelogging may be termed an “axle test”. The purpose of the axle test maybe to test the performance of an individual axle or group of axles to animpulsive load and compare the results of the performance to thestandards specified for road friendliness. The axle test may beperformed when the suspension is new in order to establish compliancewith the road friendliness criteria and to act as a reference to measurethe suspension or suspension group's compliance and wear over a periodof time.

The axle test may be conducted at various periods throughout the life ofthe suspension in order to ensure that the performance of the suspensionremains within the accepted standards. The axle test may be conductedwhile the vehicle is in service and therefore may be termed “in servicecompliance” testing. Each of the parameters may be calculated from thedata collected during any or all of the tests.

The axle test may comprise a step test in which a specified height stepdownward is used to create a negative step input to the vehiclesuspension for the purpose of determining damping ratio and fundamentalfrequency of axle-to-body bounce of the suspension. The step test may beconducted over a predetermined height step and also at a predeterminedspeed of passing over the step. The method may further allow theadaptation of the data to allow for differences in the speed and heightof the step when calculating the tested parameters.

A second test which may suitably be used in axle testing is a bump test.This test may generally comprise a series of tests performed by drivinga combination test rig vehicle over a nominal 50 mm bump (or otherpredetermined dimension) at approximately 5 km/h or at some other speed,as deemed necessary. The bump may extend upwardly or downwardly and mayprovide an approximation to a positive impulse signal applied to thesuspension of the combination test rig vehicle.

A third test which may be performed may be a road test. According tothis test, the variation in the mass signal may be recorded as thecombination test rig vehicle travels along a normal, uneven road atspeed. The speed may be up to 60 km/h or may be higher or lower ifrequired. The GPS location device may be linked to the data collected,to precisely locate the portion of road upon which the test wasconducted for future comparison of the test conditions as well as theroad condition to determine the degradation in either or both.

Any one or more of the three tests described above may be conducted inorder to assess the performance of the suspension as well as thecondition of the road itself.

According to a second particularly preferred embodiment of theinvention, the performance of the vehicle suspension system is loggedover a variable road section at different times, the position of thevehicle being identifiable at all times during the logging process.

This testing procedure may be termed a “trip test”. The trip test maypreferably allow data to be collected about the condition of the roadswhich a test vehicle travels over whilst gathering data in the form ofthe axle test for analysis, at the same time. Each trip test may beexpanded into a series of axle tests for such purposes. For example, animpulsive load may be imposed on the suspension if the test vehicledrives over a pothole in the road. If a test vehicle uses the sameroute, it would generally traverse the same pothole on different trips.By assessing the performance of the suspension in response to theimpulsive load applied to the suspension on different trips, a user maydetermine whether the pothole is getting larger or deeper or whether ithas been repaired or not.

The trip test may be triggered by the application of a particular presetmagnitude impulsive load. The test may further require that the locationof the vehicle be ascertainable with precision. This may be accomplishedusing locating means such as GPS devices linked to the system. Upontriggering the trip test, the system may begin to record the performanceof the suspension and the position of the vehicle when the test wastriggered.

Suitably, the method of the present invention may be utilised to collectand analyse data in order to log the performance of the suspension of avehicle. Individual components of the suspension may be tested or groupsof components may be tested. The system allows the logging ofinformation relating to the dynamic effect of impulsive loads applied tosuspensions and the compliance of the suspension to parameters adaptedto ascertain the effectiveness of the suspension in dampening theimpulsive load applied.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will be described with reference tothe following drawings, in which:

FIG. 1 is a schematic illustration of a typical installation of airsuspension on an articulated vehicle such as a truck and traileraccording to an embodiment of the invention.

FIG. 2 is a schematic illustration of a typical installation of a systemaccording to an aspect of the present invention on an articulatedvehicle such as a truck and trailer.

FIG. 3 is a graphical representation of a test signal returned during astep test conducted using the system according to an aspect of thepresent invention.

FIG. 4 is a graphical representation of a test signal returned during abump test conducted using the system according to an aspect of thepresent invention.

FIG. 5 is a graphical representation of the absolute value of the testsignal returned during a bump test plotted against time conducted usingthe system according to an aspect of the present invention.

FIG. 6 is a Fourier plot of a trailer axle group mass signal returnedduring testing conducted using the system according to an aspect of thepresent invention.

FIG. 7 is a schematic block diagram of a system of the invention showncoupled to other components for facilitating the downloading of datafrom the system of the invention.

FIG. 8 is a schematic block diagram of a system of the invention showncoupled to other components for facilitating the downloading of datafrom the system of the invention.

FIG. 9 is a detailed block diagram of the system of the inventionillustrated in schematic form in FIGS. 7 and 8.

DETAILED DESCRIPTION OF THE INVENTION

According to an aspect of the invention, a method for logging theperformance of a vehicle suspension system in reaction to impulsiveloads applied thereto is provided.

Generally, trucks and trailers and other heavy haulage vehicles areequipped with self-levelling suspension systems. The systems aredesigned to compensate for changes in the load by modifying thespringing or dynamic characteristics of the suspension so that thevehicle(s), always remain approximately the same height off the road,whether empty, partially loaded, or fully loaded.

The systems are designed to ensure that, even when the vehicle is fullyladen, the full upward travel of the suspension system is available forabsorbing bumps. Other related effects are things such as the headlightsare kept in proper focusing alignment, whatever the distribution of theload.

Any form of self-leveling is generally operated by one or moreload-sensing devices which measure the vertical distance between, forexample the trailer bed and the suspension arm. The greater the load,the smaller this distance tends to become. An initial variation in thedistance operates a valve which controls the height-adjusting system.Usually, height adjustment takes place at both ends of vehicle, and inparticular generally takes place at each axle or group of axles.

Air suspensions are relatively simple in principle. Collapsible,pressurized air containers take the place of conventional springs orshock absorbers; the upward movement of the wheel reduces the volume ofthe air spring, raising its pressure, so that it tries to extend itselfagain. If the air spring is inflated more, it can carry a heavier loadbefore contracting to a given height. A height-control valve connectsthe air spring to a high-pressure air reservoir when the load isincreased, and pressure is released through the valve to the atmospherewhen the load is reduced.

Air suspensions generally also comprise dampers, often referred to as“shock absorbers”. Dampers are designed to damp out vibrations so thatthe suspension does not continuously bounce up and down in response toan impulsive load. The purpose of dampers is to reduce oscillation byabsorption of energy stored in the suspension. A damper may be singleaction or double action in which damping is controlled in bothdirections.

A typical installation of the components of air suspension on anarticulated vehicle such as a truck and trailer, which are also usedaccording to the method of the present invention, is illustrated in FIG.1.

In order to control the air suspension system, the system has a meter 11connected to a power supply 12 for the system usually including abattery 14. The meter 11 is also associated with a datatransmitter/receiver 13 which is capable of transmitting data which iscaptured by the system to a remote location and receiving data and/orcommands from a remote source. An example of a remote interrogation unit15 is also illustrated in FIG. 1. This unit is adapted for use to querythe meter 11 onboard the truck when the truck is moving. Generally,radio frequency waves are used as a carrier signal to accomplish thedata transfer.

The system also has at least one and generally more than one smartamplifier 16 each associated with an air pressure transducer (APT) 17,or load cell or combinations of these, to acquire information regardingthe gross and nett weights of the vehicle. Each pressure transducer 17is associated with a component of the vehicle suspension. Generally,each APT 17 is associated with an air spring which is associated with anaxle. Each APT 17 provides feedback to the meter 11 regarding theresponse of the suspension to an impulsive load by measuring themovement of the suspension.

As stated above, each axle is generally provided with an APT 17 so thatthe movement at each axle in response to an impulsive load may bemonitored. The meter 11 and power module 12 are generally located in thetruck or prime mover of the vehicle. These components are directlyconnected to the each APT 17 associated with the truck axles.

The APT's 17 and the associated smart amplifiers 16 which monitor thetrailer axles are connected to the meter 11 and power module 12 on thetruck using a quick release connector 18 so that different trailer maybe connected to the one prime mover without loss of monitoringfunctions.

Providing the system with a handheld remote transceiver 19 allows thevehicle operator to remain safe distance from the vehicle while thevehicle is being loaded and still monitor the weights displayed on theremote receiver 19. Examples of some of the information which may becollected include gross weight, net weight, load pick up and delivery,front end weight, rear end weight, weight distribution, and massmanagement and suspension compliance testing.

The schematic layout of the components of the suspension system andelectronic weighing system which is used to implement the methodaccording to the present invention is illustrated in FIG. 2.

The truck 21 and trailer 22 are shown with smart amplifiers 16 in place.Each smart amplifier 16 is associated with the in-cab hardware whichallows a driver to monitor the performance of the suspension system ofthe truck and trailer combination which they are driving.

The smart amplifiers 16 are connected to a data logger 23. The datalogger 23 is responsible for capturing and collating all of theinformation transmitted from the smart amplifiers 16 and the associatedAPT's.

The data logger 23 is in turn associated with a computer 24 which isresponsible for the use of the raw information collected to createuseable information regarding the parameters of the suspension which areto be monitored or tested. The system is also provided with a means totransmit and/or receive data or commands to and from a remote location25, together with a locating means such as a GPS locator 26. Theanalysis of the information collected may take place at a remotelocation and the results transmitted back to the vehicle.

In use, the system collects weight information from air pressuretransducers 17 connected to air bag suspensions, and/or load cellsmounted on the vehicle. The information is then sent to the meter 11where it is displayed in kilograms of weight applied at each individualaxle or group of axles, as well as total weights. This allows theoperator to check the weights on each axle group being used, as well asthe axle group combinations and total weights as required on a displayassociated with the meter 11.

All information is date and time stamped and can be downloaded to alaptop 24 or a printer 27 in order to produce a hard copy on demand. Alldata is stored in an associated data log 23 which cannot be deletedwithout a specific set of instructions (and password) from the operator.

The applicants have subjected the system and method to testing andanalysis of the air suspension of a newly constructed, 34 tonne,four-axle trailer. The analysis is compared with the European Union (EU)requirements for “road-friendly suspensions” on heavy vehicles.Feasibility of determining road-friendliness of air suspensions forheavy vehicles without recourse to laboratory or workshop facilities wasalso explored.

The Truck & Trailer Test Rig

The truck was a standard KENWORTH® prime mover with air suspension onthe drive axles coupled to a 4-axle trailer with air suspension. This isan innovative vehicle which meets all but one of the 20 PerformanceBased Standards (PBS) as proposed currently by the National RoadTransport Commission (NRTC) specifications.

The trailer was built by O'Phee Trailers and the combination is ownedand operated by a commercial carrying service. The truck/trailercombination has been on the road since mid-February 2003 operating underpermit. One of the conditions of the permit was that the vehicle was tobe monitored for mass and position. The Gross Combination Masses (GCM)permitted is dependant on the position of the combination test rig. Thefreight task is general freight/general access when the GCM is not toexceed 42.5 tonne which is described as Higher Mass Limits (HML) and theGCM is not to exceed 50 tonne on a particular route between Acacia ridgeand Lytton in Brisbane.

The combination rig was tracked using Global Positioning System (GPS)position fixes from a C-Track GPS reporting system relayed back to abase station at the premises of Digicore Pty Ltd, a third party serviceprovider which compiled and stored the data. The C-Track system reportsevery hour via a mobile phone link. The report contains the position ofthe vehicle at various intervals on a real time basis. The prime moverwas equipped, before this trial, with the GPS reporting system for fleetmanagement purposes.

Mass data from the drive axles of the prime mover and the trailer groupis measured indirectly, but proportional to, air pressure in the highpressure air lines to the air suspension. Air pressure is converted to amass signal by a mass measurement system which sends the mass signals tothe C-Track system as well as displaying the mass of the prime mover andthe trailer on a display in the cabin. For the trailer, 40 kg incrementshave been assigned to the digital mass measurement by the massmeasurement system. The mass on the prime-mover is determined by themass measurement system apportioning a mass value to the steer axle andadding this to the measured value of air pressure on the drive groupaxle air line, proportional to the mass on that group.

It is cheaper to instrument air suspensions than steel suspensions. Tocontain capital outlay, only the drive & trailer axle groups wereinstrumented and so the steer axle was not instrumented to measure mass.However, the geometry of the combination ensured a fairly constant masson the steer axle. The trailer has a YORK® control system which raisesthe front axle when the trailer is empty and drops the axle when a loadis on board.

For the purpose of the testing, a container with freight weighingapproximately 11 tonne was loaded onto the trailer.

The Tests Applied

The Step Test

The yard of the freight operator presented an ideal opportunity toreplicate the EU step test. The EU test uses an 80 mm step down tocreate a negative step input to the vehicle suspension for purposes ofdetermining damping ratio and fundamental frequency of axle-to-/bodybounce.

A new warehouse was being built in the yard of the freight operator andthe slab was finished, awaiting the superstructure. This slab was 65 mmabove the surrounding surface of the yard manoeuvring apron. For oneseries of tests, the combination test rig was driven off the warehouseslab onto the apron at approximately 5 km/h.

The Bump Test

A second series of tests was performed by driving the combination testrig over a 50 mm nominal diameter pipe at approximately 5 km/h. The pipehad a bar welded to either end to prevent rotation as the tyres movedover it. The pipe provided an approximation to a positive impulse signalapplied to the suspension of the combination.

The On-Road Test

A final test was performed by driving the combination test rig over someroads near the freight depot. The variation in the mass signal wasrecorded as the combination test rig traveled along normal, uneven roadsat speeds up to 60 km/h.

The Results

The Step Test

The step test results plotted in FIG. 3 show that the signal is varyingslowly and gives a shape that could not be analysed easily/meaningfully.FIG. 3 shows the test signal as measured for the first 2 axles, thefirst axle signal on the left 40 and the entirety of the signal on theright (from 2.25 s to beyond 4.92s) is from the second axle. The other 2axles produced a similar shape to axle 1 and have not been included forbrevity.

The Bump Test

The bump test yielded data that lent itself to more meaningful analysisand this data is shown in FIG. 4. The three signals caused by the tyresfrom the 2^(nd), 3^(rd) and 4^(th) axles travelling over the pipe areshown in the Figure from left to right (41, 42, 43) respectively.

The second axle created the first excursion on the left of the graph.The signal generated by the first axle perturbation is not plotted hereas it was similar to the two caused by axles 3 and 4, shown as the othertwo positive excursions in FIG. 4.

The On-Road Test

The variation in the mass signal from the trailer axle group was ofprimary interest for this evaluation. A sample of how the data appearsin hexadecimal format, this example from the on-road test appears below.

89 88 87 86 84 83 81 00 02 04 07 09 0C 0E 2A 02 05 07 09 0B 0C 0D 0D 0D0D 0D 0D 0D 0D 0C 0B 09 07 05 03 01 00 82 84 86 89 8B 8D 8F 88 81 83 8586 87 89 89 8A 8B 8B 8B 8B 8B 8B 8B 8B 8B 8B 8A 89 87 86 84 82 00 02 0407 0A 0D 23 02 05 08 0A 0C 0D 0D 0E 0D 0D 0D 0D 0D 0D 0D 0C 0C 0A 08 0604 02 00 82 85 87 8A 8C 8E 80 82 84 85 87 89 8A 8B 8B 8C 8C 8C 8C 8C 8C8C 8B 8A 89 88 87 85 83 81 00 03 05 08 0B 0E 27 02 05 07 09 0A 0A 0A 0A0A 0A 0A 09 09 09 07 06 04 02 00 81 83 86 88 8B 8D 8F F4 82 84 85 87 8989 8A 8A 8B 8B 8B 8B 8B 8B 8B 8A 89 88 87 86 84 83 81 00 02 05 08 0A 0D0F 26 02 03 05 06 07 07 07 07 07 07 07 07 06 05 04 02 00 81 84 86 88 8A8D 8F 84 81 83 85 86 88 89 8B 8C 8C 8D 8D 8D 8D 8D 8D 8D 8D 8D 8C 8B 8988 86 84 82 00 01 04 06 09 0B 0E 24 02 04 06 07 09 09 09 09 09 09 09 0908 08 06 05 03 00 81 83 86 88 8B 8D 8F F6 82 83 85 86 88 89 8A 8B 8B 8B8B 8B 8B 8B 8B 8B 8B 8A 88 87 85 84 82 00 01 04 06 09 0C 0E 1D 02 04 0506 07 07 07 07 07 07 07 07 07 06 05 04 03 01 00 81 83 85 87 89 8B 8D 8FF3 81 83 85 86 87 89 89 8A 8A 8A 8A 8A 8A 8A 8A 8A 89 88 86 85 83 82 0002 04 06 09 0B 0E 0E 02 04 05 07 08 08 09 09 08 08 08 08 07 06 04 02 0081 84 86 89 8B 8D 8F E0 81 83 85 86 87 88 89 89 89 89 89 89 89 89 89 8887 86 85 83 82 00 01 03 05 08 0A 0D F4 02 04 06 08 09 0A 0B 0B 0A 0A 0A0A 0A 09 07 05 03 01 81 83 85 88 8A 8C 8E E4 81 83 84 85 85 86 86 86 8686 86 86 86 86 85 85 84 83 82 81 00 01 02 04 05 07 09 0B 0D 0F 16 02 0405 07 08 09 09 09 09 08 08 08 07 06 04 03 01 81 83 85 87 8A 8C 8E 85 8183 84 85 86 87 88 88 88 88 88 88 88 88 88 88 88 87 86 85 84 82 81 00 0103 05 07 09 0C 0E 0F 35 01 02 03 04 04 04 04 04 04 04 03 03 02 00 00 8284 86 88 8A 8C 8E 8F 8B 81 83 84 85 87 88 88 89 89 89 89 89 89 89 89 8989 88 88 87 86 85 83 82 00 00 02 04 06 08 0A 0C 0E 1C 01 03 04 04 05 0505 04 05 05 04 04 03 02 00 81 83 85 87 89 8B 8D 8F F7 81 83 84 85 87 8889 8A 8A 8A 8A 8B 8B 8B 8B 0F B8

The data from the tests was converted and a plot of the variation inmass induced by the dynamic forces on the combination was produced asFIG. 6.

Analysis

The Step Test

The step test did not yield any data that could be analysed in ameaningful way. It is noted that the EU test differs from the step testconducted in that it is usually conducted at a much a higher speed thanthose used for this testing, it is done for one axle only and the dropis 80 mm, not 65 mm as used for this testing. The applicants surmisethat the effect of the air lines equalising the pressure differentialbetween the air bags on differing axles caused the signal to behave inthe manner shown in FIG. 3, particularly for axle 2. It was thought thatthe 3 axles were restraining the first axle in the vertical plane as itwent over the step but when the second axle encountered the step theapplicants thought that that was the point of equilibrium of the axlegroup and the group then teetered like a see-saw, giving the resultantaberrant signal. The applicants also surmise that this was why the EUtest was performed with only one axle and at relatively higher speeds.

The Bump Test

By taking the absolute values the data from the first perturbation inFIG. 4, that is, the first and third excursions of the mass signal, thedamping ratio (ζ) may be determined using the formula:ζ=δ/√(δ²+(2π)²)where δ is the standard logarithmic decrement given by the following:

$\delta = {\ln( \frac{A_{1}}{A_{2}} )}$andA₁=amplitude of the first peak 44 in the plot of the absolute value ofthe response andA₂=amplitude of the third peak 45 in the plot of the absolute value ofthe response.

From FIG. 5, it can be seen that the value of A₁=6 and A₂=1. It is notedthat these values are the closest approximation to the actual valuesmeasured by the mass measurement system given the approximately 1000digitisation steps over the measurement range of 40 T: (40000 kg/1000=40kg increments).

Substituting the measured values of A₁ and A₂ yields a damping ratio (ζ)of 0.27 or 27%, allowing for the error described above.

The EU Standard is 20% or greater so it can be seen that this trailermeets the EU Standard for “road-friendly suspension” dampers. Further,this exercise shows that, by using a simple test of driving over a 50 mmpipe and analysing the data provided by the on-board mass measurementsystem, the damping ratio may be determined by simple calculation.

The On-Road Test

By subjecting the data from the on road test to Fourier analysis, thesystem is able to determine the trailer's body-to-axle-group frequenciesinduced by the dynamic forces on the combination. For this analysis, itwas assumed that the signal derived from driving the vehicle on normalroads approximated to a random signal. Fourier analysis of an output, orderived, signal after it has been generated from a random input signalof uniform amplitude to any system allows determination of the transferfunction of the system as expressed by the frequencies present in theoutput signal.

The plot illustrated in FIG. 6 is a Fast Fourier Transform (FFT) thatis, by definition, lumpy and does not yield pure and clean plots on themagnitude axis. Even allowing for the overall noise created by the FFTprocess, it can be seen that the greatest frequency magnitude 46 presentin the FFT of the on-road signal is that of 1.5 Hz-2 Hz. Given that theEU standard for body bounce is >2.0 Hz, it is statistically probablethat this parameter is met by the suspension tested and reflected onthis plot. It is to be noted that some lower frequencies appear to bepresent and that there are greater magnitude frequencies at approx. 4Hz, 8 Hz and 15 Hz. Axle hop appears to be the explanation for the 15 Hzsignal. Further research is needed for the 4 & 8 Hz signals.

FIG. 7 shows a system 30 of the invention coupled to an on-boardpersonal computer (OBPC) 31, OBPC 31 is connected to an RF transmitter32. Transmitter 32 allows data from the system 30 to be downloaded via aradio link. A printer 32 is connected to the OBPC 31. A docking station33 allows a host computer 34 to be coupled to the OBPC 31 or devicesother than a computer 34 to be connected to OBPC 31. Computer 34 maydownload data from the system 30.

FIG. 8 shows a block diagram of an alternative way to that of FIG. 7 inwhich a system 30 may be coupled to other components to allow data to bedownloaded from the system 30. A serial memory unit (SMU) 40 is coupledto the system 30. A printer 41 and various communication devices 42 areconnected to SMU 40. An on-board personal computer (OBPC) 43 isconnected to the SMU 40 and this OBPC 43 is coupled to an RF transmitter44 and a docking station 45. The docking station 45 allows a hostcomputer 46 or other devices to be coupled to the OBPC 43 fordownloading data. A memory unit 47 may be coupled to the computer 46 toprovide for data downloaded from the system 30 to be backed up in caseof failure of the OBPC 43.

The AAU illustrated in box 47 with an additional SMU, providesadditional data back-up capabilities at the same time providingadditional serial data ports to connect to various peripheral deviceswhich are used by various operators of this system in variousapplications or end uses. The SMU/AAU 47 is also used to store the datawhich is collected when performing the tests.

FIG. 9 is a detailed block diagram of the system of the inventionillustrated in schematic form in FIGS. 7 and 8.

In the present specification and claims, the word “comprising” and itsderivatives including “comprises” and “comprise” include each of thestated integers but does not exclude the inclusion of one or morefurther integers.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearance of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more combinations.

In compliance with the statute, the invention has been described inlanguage more or less specific to structural or methodical features. Itis to be understood that the invention is not limited to specificfeatures shown or described since the means herein described comprisespreferred forms of putting the invention into effect. The invention is,therefore, claimed in any of its forms or modifications within theproper scope of the appended claims appropriately interpreted by thoseskilled in the art.

1. A method for logging the performance of a vehicle suspension systemby testing dynamic performance of at least one vehicle suspension systemcomponent, the method including the steps of: a. measuring the dynamicexcursion of mass of an impulsive load with an electronic weighingsystem in response to a unit impulsive load, wherein the electronicweighing system is mounted onboard the vehicle and monitors the at leastone suspension system component, and b. measuring an oscillationfrequency of said at least one vehicle suspension system component inresponse to said unit impulsive load, and c. determining the dampeningratio of the at least one vehicle suspension system component using thedynamic excursions of mass, and the maximum oscillation frequency of theat least one vehicle suspension system component.
 2. The methodaccording to claim 1 wherein the electronic weighing system mounted onboard the vehicle includes at least one load measuring element,associated with one or more vehicle suspension system components, eachload measuring element associated with a signal amplifier, each signalamplifier associated with a central power module and a meter to displaycollected information.
 3. The method according to claim 2 wherein thesignal amplifiers used are adapted to store measurements collected bythe step of measuring the dynamic excursion of mass and the step ofmeasuring an oscillation frequency during a calibration test.
 4. Themethod according to claim 2 wherein a central meter is provided to whichall load measuring elements transmit data.
 5. The method according toclaim 2 wherein the meter is a multi-channel meter adapted to receiveinformation on multiple channels, each of the channels adapted toreceive data from an axle grouping.
 6. The method according to claim 5wherein up to eight load measuring elements provide information to themeter on each channel.
 7. The method according to claim 2 wherein theelectronic weighing system includes an on-board storage device toreceive and record all information from all associated load measuringelements.
 8. The method according to claim 7 wherein the on-boardstorage device includes a data log allowing the tracking of theinformation collected according to dates, times, and particular dynamicparameters comprising G-force and time, both of which can be eitherpre-set or varied to suit particular operating conditions.
 9. The methodaccording to claim 2 wherein the meter is adapted for communication witha tool for analysis of the collected information, and is associated witha communication means for transmitting and/or receiving information. 10.The method according to claim 2 further including a plurality ofvehicles, each of said plurality of vehicles provided with a vehiclelocating means.
 11. The method according to claim 2, wherein theelectronic weighing system further includes one or more remoteinterrogation units adapted to allow remote access to the meter providedin a vehicle, the remote interrogation units allowing the viewing and/oranalysis of information collected.
 12. The method according to claim 1wherein the performance of the vehicle suspension system is logged overa standard road section at different times to test the performance of anindividual axle or group of axles to an impulsive load.
 13. The methodaccording to claim 12 including the step of comparing the performance ofthe vehicle suspension system to predetermined standards.
 14. The methodaccording to claim 12 wherein the performance of the vehicle suspensionsystem when the at least one vehicle suspension system component is new,is compared to performance at various periods throughout the life of theat least one vehicle suspension system component in order to ensure thatthe performance of the at least one vehicle suspension system componentremains within predetermined standards.
 15. The method according toclaim 12 including a step test in which a specified height step downwardis used to create a negative step input to the vehicle suspension systemcomponent for the purpose of determining damping ratio and fundamentalfrequency of axle-to-body bounce of the suspension.
 16. The methodaccording to claim 15 wherein the step test is conducted over apredetermined height step and also at a predetermined speed of passingover the step.
 17. The method according to claim 16 further allowing theadaptation of measurements collected by the step of measuring thedynamic excursion of mass and the step of measuring an oscillationfrequency to allow for differences in the speed and height of thepredetermined height step when calculating the tested parameters. 18.The method according to claim 12 including a series of tests performedby driving the vehicle over a 50 mm bump at approximately 5 km/h toprovide an approximation to a positive impulse signal applied to thesuspension of the vehicle.
 19. The method according to claim 12including a test in which the variation in a mass signal is recorded asthe vehicle travels along a normal, uneven road.
 20. The methodaccording to claim 19 wherein a location device is linked to themeasurements collected by the step of measuring the dynamic excursion ofmass and the step of measuring an oscillation frequency, to preciselylocate the portion of road upon which the test was conducted for futurecomparison.
 21. The method according to claim 12 wherein the performanceof the vehicle suspension system is logged over a variable road sectionat different times, the position of the vehicle being identifiable atall times during the logging process, allowing data to be collectedabout the condition of the roads which the vehicle travels over.
 22. Themethod according to claim 21 wherein the logging is triggered by theapplication of a particular preset magnitude impulsive load.
 23. Themethod according to claim 22 wherein the location of the vehicle isascertainable with precision using a locating means.
 24. The methodaccording to claim 1 wherein the impact loading of the vehicle isdetermined.